A United Boeing 767-400, registration N68061 performing flight UA-53 from Zurich (Switzerland) to Washington Dulles,DC (USA), was climbing out of Zurich when the crew stopped the climb at about FL200, descended the aircraft to FL100 and prepared for an immediate return to Zurich's runway 16, emergency services prepared to take their stand by positions at runway 16. While returning to Zurich at FL100 the crew decided to not perform an overweight landing, emergency services returned to their stations. The crew descended the aircraft to FL080 to dump fuel for about 45 minutes and landed on Zurich's runway 16 about 2 hours after departure. The crew reported normal operations and taxied to the apron. The flight was cancelled. The occurrence aircraft is still on the ground in Zurich about 8 hours after landing.